Arrangement for ensuring the function of a vehicle brake

ABSTRACT

The invention relates to an arrangement ( 11 ) for ensuring the functionning of a brake configuration for a vehicle with a multiplicity of wheels which are arranged with reference to a front axle and at least one rear axle and which support the vehicle, the brake configuration incorporating at least two brake devices ( 5   a - f ), each of them designed to act upon one of said wheels, and a brake control ( 12 ) with which the brake devices ( 5   a - f ) can be activated with a total brake action. The arrangement ( 11 ) incorporates a memory unit ( 14 ) designed to store at least one value of a parameter for said brake devices, said parameter relating to at least one previous braking operation performed by the respective brake device ( 5   a - f ), and a control unit ( 13 ) designed to distribute said brake action to said brake devices ( 5   a - f ), taking into account the value of said parameter of the respective brake devices ( 5   a - f ) when the brake control ( 12 ) is actuated. Said brake devices ( 5   a - f ) preferably consist of disc brakes and the value of said parameter indicates to what extent a film has accumulated on the brake lining surfaces which come into contact with the respective discs, which film reduces the friction between discs and brake linings at least incipiently. If the value indicates that such a film has formed, the whole or a major portion of the brake action called for by the driver, i.e. the total brake action, is distributed to the disc brakes ( 5   a - f ) whose value of said parameter indicates the presence of such a film.

BACKGROUND TO THE INVENTION, AND STATE OF THE ART

[0001] The present invention relates to an arrangement for ensuring thefunctioning of a brake configuration for a vehicle according to thepreamble to patent claim 1.

[0002] That the brakes of a vehicle, e.g. a heavy vehicle, function asintended is of the greatest importance, particularly today, when thetotal weights of heavy vehicle combinations (e.g. truck and trailer) areincreasing and hence also the axle pressures of the respective vehiclecombinations. In addition, average speeds are higher and timetablestighter. Traffic density is increasing. All this results in heavydemands upon the brake systems of heavy vehicles, particularly that theyshould function as intended.

[0003] Conventional trucks use pneumatic configurations for controllingthe braking process. More recent trucks use electronics for controllingthe braking process. Compressed air is only used for applying the wheelbrakes, which may include disc brakes or drum brakes, one wheel brakefor each wheel. The driver of a heavy vehicle can communicate with theelectronically controlled brake system via some brake control,preferably the brake pedal. Such electronically controlled brake systemsmay also incorporate load sensors designed to measure, for example, thevehicle's respective axle weights or total weight. The electronicallycontrolled brake system is designed to communicate with the pneumaticconfiguration which is designed to control the brake cylinders of therespective wheel brakes. The brake cylinders are connected to thefriction linings of the respective wheel brakes which are intended toact upon, for example, a brake disc or a brake drum. In suchelectrically controlled brake systems, all the wheel brakes are usuallyapplied simultaneously. However, the brake system may be designed insuch a way that the brake pressure delivered to one wheel brake of thevehicle differs from the brake pressure delivered to another wheel brakeof the same vehicle, with a view to maintaining vehicle stability. Thismethod is used in order, inter alia, to prevent skidding and overturningof the vehicle, e.g. if the brake action called for by the driver on asharp bend would result in too much brake action on an individual axle,the brake system may be designed in such a way that the brake actioncalled for is limited. Electronically controlled brake systems of theaforesaid type may also incorporate ABS control, i.e. the brake actioncalled for by the driver being limited by the available friction betweenground and tires with a view to preventing wheel locking. In addition,an electronic brake system of the aforesaid type may incorporatefunctions to prevent wheel spin. Many electronically controlled brakesystems incorporate at least one additional brake, e.g. a retarder whichgenerates an outward braking moment by means of, for example, viscousfriction. Such a retarder may be arranged to brake the universal shaftof the vehicle concerned. Further examples of supplementary brakes whichmay be included in an electrically controlled brake system are exhaustbrakes and compression brakes which increase the engine's naturalbraking effect.

[0004] Light braking and recurring light braking by means of the wheelbrakes, particularly where the wheel brakes incorporate disc brakes, mayreduce the friction between discs and linings. This may lead to thedriver finding the vehicle difficult to brake and hence possibly to thedriver pressing the brake pedal harder, which may lead to unnecessarilygreat brake action, so-called overbraking.

[0005] Said reduction in friction between discs and brake liningsdepends on the brake lining material. The reduction in friction may bedue, inter alia, to changes in the brake lining material which may arisebecause of low thermal and mechanical loading, particularly during lightbraking. This may result in the formation of a film which accumulates onthe brake lining surfaces. The film accumulating on the brake liningsurfaces which make contact with the disc causes reduction in frictionbetween discs and brake linings. It is also possible for brake liningmaterial to react with the road surface, e.g. with salts, in which casea film may form and accumulate on the brake lining surfaces and hencereduce the friction between discs and brake linings. Said film may thus,at least at an initial stage of brake application, reduce frictionbetween brake linings and brake devices.

SUMMARY OF THE INVENTION

[0006] The object of the present invention is to provide an arrangementby which the problems associated with reduced friction between discs andlinings of a disc brake are eliminated.

[0007] This object is achieved with the arrangement indicated in theintroduction which has the features defined in the characterising partof patent claim 1.

[0008] Such an arrangement, which may incorporate a computer and isdesigned to store at least one value of a parameter for each brakedevice, said parameter being related to at least one previous brakingoperation performed by the respective brake device, makes it possible bymeans of the control unit to distribute the brake action called for bythe driver to said brake device, taking into account the value of saidparameter of the respective brake device. Said parameter which relatesto at least one previous braking operation performed by the respectivebrake device may be created in various ways. In addition, the value ofthe parameter of the respective brake device indicates the extent towhich any film has accumulated on the brake linings of the respectivebrake device. This will be discussed in more detail below. Particularlyin the case of disc brakes there is a tendency for a film to be able toaccumulate on the linings of disc brakes and reduce the friction betweendiscs and brake linings, resulting in the disc brakes not being able toprovide maximum brake action. When the value of the parameter of arespective brake device indicates that a film has accumulated on thebrake lining surfaces, particularly the contact surfaces, the controlunit of the arrangement may be designed to deliver a larger proportionof the brake action called for by the driver to that brake device.Delivering a larger proportion of the brake action to that brake devicewill result in the development of a higher temperature than if the brakeaction was uniformly distributed over all the brake devices. This highertemperature is capable of removing said film, and consequently the brakedevice concerned can thereafter provide maximum brake action. It shouldbe noted that the arrangement according to the invention may be appliedon vehicles whose wheel brakes consist of both drum brakes and discbrakes, but brake devices in said patent application refers preferablyto disc brakes.

[0009] As mentioned above, said parameter may be created in various waysand the arrangement according to the invention incorporates meansdesigned to calculate the value of said parameter. According to oneembodiment of the invention, said parameter is formed on the basis ofthe actual brake action from the respective brake device and the desiredbrake action from the respective brake device. A braking operation mayentail different brake pressures being delivered to the various wheelbrakes, inter alia in order, as previously mentioned, to maintainvehicle stability. In addition, the desired brake action from therespective wheel brake, i.e. the brake action expected from therespective wheel brake when a certain brake pressure is delivered to it,is calculated on the basis of the vehicle's weight and the brakepressure delivered to the respective wheel brake. The vehicle's actualbrake action, i.e. the brake action resulting from the brake pressuredelivered, may thus differ from the desired brake action. Thisdifference may be due to a film having accumulated on the brake liningsurfaces of the respective wheel brake which are intended to abutagainst, for example, a disc. The film reduces the friction betweenbrake linings and discs and prevents the achievement of desired brakeaction. The actual brake action may be calculated, e.g. on the basis ofthe retardation of the wheel which the respective brake device isintended to act upon. According to a further embodiment of theinvention, said parameter is formed on the basis of brake power suppliedto the respective brake device and the time when said brake power isdelivered to the respective brake device. Low brake pressure deliveredto a certain brake device for a prolonged period is a particular case ofrisk that a film of the aforesaid kind may form on that brake device.

[0010] According to a further embodiment of the invention, the controlunit incorporates a comparison unit in which a predetermined value ofsaid parameter is stored, and if the value of said parameter of one ofthe respective brake devices corresponds to or exceeds saidpredetermined value the control unit is designed to distribute the wholeor a major portion of said brake action to that brake device when thebrake control is actuated.

[0011] Consequently and as mentioned previously, the control unit may bedesigned to distribute the whole or a major portion of the brake actioncalled for by the driver to the brake device whose value of saidparameter is the most critical. If the value of said parameter for allthe brake devices corresponds to or exceeds said predetermined value,the control unit may be designed to distribute the whole or a majorportion of said brake action to one of said brake devices at a time. Thepurpose of this is to enable the heat developed at the time of brakingto eliminate the film accumulated on the brake lining surfaces of therespective brake device, after which that brake device can providemaximum brake action. According to a further embodiment of theinvention, the control unit may be designed to distribute the whole or amajor portion of said brake action to that brake device upon recurringactuation of the brake control.

[0012] According to one embodiment of the invention, the brakeconfiguration incorporates at least four brake devices, each of themdesigned to act upon one of said wheels. All the wheels of heavy trucksmay be provided with a disc brake. According to one embodiment of theinvention the control unit is designed to distribute the whole or amajor portion of the brake action called for by the driver (also calledthe total brake action in said patent application) to the brake devicewhich is arranged on the axle which includes the wheel which the brakedevice whose value of said parameter corresponds to or exceeds saidpredetermined value is designed to act upon. Distributing the brakeaction to the brake devices on one and the same axle maintains thevehicle's stability.

[0013] The object of the arrangement is, as previously mentioned, toensure the functioning of a brake configuration of a vehicle, i.e., aspreviously mentioned, to ensure that respective disc brakes can providethe desired brake action. To make this possible, the control unit isdesigned to distribute the brake action called for in proportion to thevalue of said parameter of respective brake devices. However, thedistribution of brake action does not take place in such a way as tojeopardise the vehicle's stability, as the magnitude of the brake actiondistributed to the respective brake devices is limited in such a way asto maintain the vehicle's stability. The brake action distributed to therespective brake devices is also limited in such a way as to take intoaccount the available friction between ground and tires.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will now be explained by describing apreferred embodiment with reference to the attached drawings.

[0015]FIG. 1 depicts schematically a brake configuration for a heavyvehicle and

[0016]FIG. 2 depicts schematically an embodiment of an arrangementaccording to the present invention.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

[0017]FIG. 1 depicts schematically a brake configuration of a heavyvehicle such as a truck with a multiplicity of wheels 1 a-f which arearranged with reference to a front axle 2 and two rear axles 3, 4 andwhich support the vehicle. The brake configuration of the vehicleincludes a main brake which incorporates brake devices 5 a-f designed toact upon the vehicle's wheels 1 a-f. The brake devices 5 a-f may includepneumatic disc brakes, in which case the main brake includes theequipment required for applying the brake linings of the respective discbrakes to the discs which rotate with the respective wheels 1 a-f. Thebrake configuration of the vehicle includes a supplementary brake in theform of a retarder 6 which generates outward braking moment by means ofviscous friction. The retarder 6 is connected to the universal shaft 7and the vehicle's gearbox 8 and only brakes the powered wheels 1 c-d. Inaddition, the vehicle incorporates a further supplementary brake in theform of an exhaust brake 9. The exhaust brake 9 is connected to thevehicle's engine 10.

[0018]FIG. 2 depicts an arrangement 11 for controlling the brakeconfiguration of a heavy vehicle such as a truck according to anembodiment of the invention. Only the wheel brakes, i.e. in this casethe brake devices 5 a-f which include disc brakes and the retarder 6 ofthe brake configuration appear in FIG. 2. It should be noted that thebrake configuration might also include the exhaust brake 9. Reference 12denotes a brake control which may incorporate the brake pedal by whichthe brake devices 5 a-f and the retarder 6 can be activated and by meansof which a driver can call for a brake action of the vehicle, aso-called total brake action of the vehicle. The arrangement 11 includesa control unit 13 which may incorporate a computer, a memory unit 14, acomparison unit 15, computing means 16 and a sensor 17. How theconstituent parts of the arrangement 11 according to FIG. 2 cooperatewill be described in more detail later on in the description. It shouldbe noted that the arrangement 11 according to the invention is alsoapplicable to other types of vehicle, e.g. passenger cars, other typesof freight vehicles, buses and similar utility vehicles.

[0019] The brake pedal 12 defines the brake action of the vehicle calledfor by the driver, i.e. the total brake action of the vehicle. Thesensor 17 is designed to continuously detect the brake action called forby the driver and transmit to the control unit 13 a signal whichcorresponds to the total brake action.

[0020] Upon light braking, the control unit 13 may be designed todistribute the whole of the brake action called for by the driver to theretarder 6. However, the control unit 13 may be designed also todistribute the brake action to the disc brakes 5 a-f. Light braking of avehicle by means of disc brakes entails risk that a film may accumulateon brake lining contact surfaces as previously mentioned in theintroductory description, resulting in the disc brakes not providing thedesired brake action. To ensure that the disc brakes 5 a-f function asintended, the computing means 16 are designed to calculate a value of aparameter for all the disc brakes 5 a-f, which parameter relates to atleast one previous braking operation performed by the respective discbrakes 5 a-f. The parameter may be formed in various ways. The parametermay be formed on the basis of the actual brake action from respectivebrake devices 5 a-f and the desired brake action from respective brakedevices 5 a-f. The desired brake action, i.e. the brake action expectedfrom a respective wheel brake when a certain brake pressure isdistributed to it, may be calculated on the basis of the brake pressuredelivered to respective disc brakes 5 a-f and the vehicle's actualweight with reference to respective disc brakes 5 a-f. At the same time,load sensors 18, only one of which appears in FIG. 2, may be designed todetect the axle load of respective disc brakes 5 a-f. The control unit13 and the computing means 16 are thus designed to communicate with saidload sensors 18. The actual brake action from respective disc brakes 5a-f, i.e. the brake action resulting from the brake pressure deliveredto respective disc brakes 5 a-f, may thus differ from the desired brakeaction. This difference may be due to a film having accumulated on thebrake lining surfaces of the respective disc brake which are intended toabut against the disc. The actual brake action may for example becalculated on the basis of the retardation of the wheel 1 a-f which therespective disc brake 5 a-f is intended to act upon. At the same time,detection means 19, only one of which for one of the respective wheelsappears in FIG. 2, are designed to detect the retardation of therespective wheels 1 a-f. Thus the control unit 13 and the calculatingmeans 16 are designed to communicate with said detection means 19. Afurther way of forming said parameter may be on the basis of brake powersupplied to respective disc brakes 5 a-f and the time when said brakepower is delivered to respective brake devices 5 a-f.

[0021] On the occasion of a braking operation the computing means 16 aredesigned to calculate a value of the parameter for respective discbrakes 5 a-f. These values are stored in the memory unit 14. At the timeof the next braking operation the comparison unit 15, in which apredetermined value of said parameter is stored, is designed to comparethe value stored in the memory unit 14 of the parameter of respectivedisc brakes 5 a-f with the predetermined value, and if a value of theparameter of one of the disc brakes 5 a-f corresponds to or exceeds thepredetermined value, the control unit 13 may be designed to distributethe whole or a major portion of the brake action called for by thedriver, i.e. the total brake action, to that disc brake. Consequentlythe brake linings of that disc brake will be applied with greater force,resulting in the development of a higher temperature capable of removingthe film accumulated on that disc brake's linings. The magnitude of thebrake action distributed by the control unit 13 to a disc brake 5 a-f islimited in such a way as, inter alia, not to jeopardise the vehicle'sstability. The control unit 13 may possibly be designed to distributethe whole or a major portion of the brake action to the disc brakeswhich are arranged with reference to one and the same axle 2, 3, 4 inorder to avoid jeopardising the vehicle's stability.

[0022] The invention is not limited to the embodiment depicted but maybe varied and modified within the scopes of the ensuing patent claims.

1. Arrangement (11) for ensuring the functioning of a brakeconfiguration for a vehicle with a multiplicity of wheels (1 a-f) whichare arranged with reference to a front axle (2) and at least one rearaxle (3, 4) and which support the vehicle, the brake configurationincorporating two brake devices (5 a-f), each of them designed to actupon one of said wheels (1 a-f), and a brake control (12) by which thebrake devices (5 a-f) may be activated with a total brake action,characterised in that the arrangement (11) includes a memory unit (14)designed to store at least one value of a parameter for said brakedevices (5 a-f), said parameter relating to at least one previousbraking operation performed by the respective brake devices (5 a-f), anda control unit (13) designed to distribute said brake action to saidbrake devices (5 a-f), taking into account the value of said parameterof the respective brake devices (5 a-f) at the time of actuating thebrake control (12).
 2. Arrangement (11) according to claim 1,characterised in that the arrangement (11) incorporates means (16)designed to calculate the value of said parameter.
 3. Arrangement (11)according to claim 2, characterised in that said parameter is formed onthe basis of the actual brake action from respective brake devices (5a-f) and the desired brake action from respective brake devices (5 a-f).4. Arrangement (11) according to any one of the foregoing claims,characterised in that said parameter is formed on the basis of brakepower supplied to respective brake devices (5 a-f) and the time whensaid brake power is delivered to respective brake devices (5 a-f). 5.Arrangement (11) according to any one of the foregoing claims,characterised in that the control unit (13) incorporates a comparisonunit (15) in which a predetermined value of said parameter is stored,and if the value of said parameter of one of the respective brakedevices (5 a-f) corresponds to or exceeds said predetermined value thecontrol unit (13) is designed to distribute the whole or a major portionof said brake action to that brake device (5 a-f) when the brake control(12) is actuated.
 6. Arrangement (11) according to claim 5,characterised in that if the value of said parameter for all the brakedevices (5 a-f) corresponds to or exceeds said predetermined value thecontrol unit (13) is designed to distribute the whole or a major portionof said brake action to one of said brake devices (5 a-f) at a time. 7.Arrangement (11) according to either of claims 5 and 6, characterised inthat the control unit (13) is designed to distribute the whole or amajor portion of said brake action to that brake device (5 a-f) uponrecurring actuation of the brake control (12).
 8. Arrangement (11)according to claim 5, whereby the brake configuration includes at leastfour brake devices (5 a-f), characterised in that the control unit (13)is designed to distribute the whole or a major portion of said brakeaction to the brake devices (5 a-f) which are arranged on the axle (2,3, 4) which incorporates the wheel (1 a-f) which the brake device (5a-f) whose value of said parameter corresponds to or exceeds saidpredetermined value is designed to act upon.
 9. Arrangement (11)according to any one of the foregoing claims, characterised in that themagnitude of said brake action is limited in such a way as to maintainthe vehicle's stability.
 10. Arrangement (11) according to any one ofthe foregoing claims, characterised in that said brake devices (5 a-f)include disc brakes.